1. What is Absolute Risk Reduction?

Absolute Risk Reduction (ARR) is the difference in event rates between control and treatment groups in clinical trials. It represents the absolute benefit of a treatment compared to control.

2. How Does the Calculator Work?

The calculator uses the ARR approximation formula:

Where:

• \( ARR \) — Absolute Risk Reduction (proportion)
• \( CER \) — Control Event Rate (proportion)
• \( HR \) — Hazard Ratio (ratio)

Explanation: This formula approximates the absolute risk reduction when given the control event rate and hazard ratio from survival analysis.

3. Importance of ARR Calculation

Details: ARR provides a clinically meaningful measure of treatment effect that is easier to interpret than relative measures like hazard ratio. It helps in calculating Number Needed to Treat (NNT).

4. Using the Calculator

Tips: Enter control event rate as a proportion (0-1), hazard ratio as a positive number. CER must be between 0 and 1, HR should be ≥0.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between ARR and RRR?
A: ARR is the absolute difference in event rates, while RRR (Relative Risk Reduction) is the proportional reduction relative to control group risk.

Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) = 1/ARR. It represents how many patients need to be treated to prevent one additional bad outcome.

Q3: When is this approximation most accurate?
A: This approximation works best when event rates are low and follow-up times are similar between groups.

Q4: What are typical ARR values in clinical trials?
A: ARR values vary widely by condition and treatment. Values of 0.01-0.10 are common, with higher values indicating more effective treatments.

Q5: Can ARR be negative?
A: Yes, negative ARR indicates the treatment is harmful compared to control (increased risk of the outcome).